Method of producing by casting a piston with a cooled ring carrier

ABSTRACT

To prevent, in a cooled ring carrier ( 1 ) for pistons, durinh Alfin bonding, the formation of oxides induced by air that escapes due to porous ring carrier material and, as a consequence, an impairment of the ring carrier bond. To this end, the cooled ring carrier, once the ring carrier part and the sheet metal part ( 3 ) have been linked, is subjected to negative pressure in a vacuum tank.

[0001] The invention relates to a method for producing a piston with acooled ring carrier, consisting of a ring carrier part and a sheet-metalpart linked with it.

[0002] Such a ring carrier and a corresponding production method areknown from DE 19750021. The cooled ring carrier is Alfin-bonded in analuminum-base melt before having the piston material cast around it.During Alfin bonding, a layer of iron aluminides forms on the iron basematerial, which layer serves as a bonding layer between the aluminummaterial and the iron material of the ring carrier in the piston. Thering carrier part normally consists of a Niresist material with alamellar graphite structure.

[0003] It has now been shown that during Alfin bonding of the cooledring carrier, the gas pressure in the cooling channel increases and,since the ring carrier material is not always present in pore-free form,that in an individual case, surprisingly, entrapped air can actuallyescape from the cooling channel. This results in the formation of oxideskins in the Alfin bath, which skins adhere to the cooled ring carrierand represent defects in the ring carrier bond on the finished piston.

[0004] The invention therefore deals with the problem of preventingdefects in the ring carrier bond of cooled ring carriers.

[0005] This problem is solved, in a method according to the preamble, bymeans of the characterizing feature of claim 1. Advantageous furtherdevelopments are the object of the dependent claims.

[0006] Linking of the ring carrier part and the sheet-metal part issupposed to take place by means of a linking method that is normallygas-tight, for example by means of welding or soldering.

[0007] As a result of the application of negative pressure, airentrapped in the cooling channel can escape, if the material of the ringcarrier is porous, and the formation of excess pressure during Alfinbonding is prevented.

[0008] The invention will be explained in greater detail in thefollowing. The drawing shows:

[0009]FIG. 1 a cooled ring carrier in the welded state.

[0010] The cooled ring carrier 1 consists of a ring carrier part 2 and asheet-metal part 3 welded to the former, which jointly form a coolingchannel 4 of a diesel piston.

[0011] Since the material of the ring carrier is not gas-tight in allcases, it can happen that during Alfin bonding of the cooled ringcarrier, gas evolution and the formation of oxides and bubbles mighttake place, thereby damaging the ring carrier bond.

[0012] In order to avoid this, negative pressure is applied to thecooled ring carrier 1 or a plurality of ring carriers in a vacuum tank.The negative pressure can be 10 mbar, for example. Depending on thenumber of non-tight ring carriers, and as a function of the containervolume, the negative pressure can increase to 20-50 mbar after sometime.

[0013] In order to ensure pressure equalization in the case of thenon-tight ring carriers, the ring carriers must remain in the evacuatedvacuum tank for a minimum period of time, for example 24 hours.

[0014] A high level of productivity can furthermore be reached if aplurality of vacuum tanks filled with cooled ring carriers is evacuatedat the same time, in a larger vat. This can be done in that the vacuumtanks have a lid that rests loosely against a rubber gasket.

[0015] During evacuation of the vat to a negative pressure of 10 mbar,for example, air can escape from the vacuum tanks because the lids restloosely against the gaskets. As soon as the vat is vented, the lid formsa seal against the rubber gasket, so that the vacuum tank remainsevacuated. The vacuum tank is not vented until just before removal ofthe cooled ring carriers, by way of a valve, and the ring carriers aredipped into the Alfin bath as soon as possible after being removed, inorder to prevent air from flowing back into the non-tight ring carriers.

[0016] The vacuum tanks can be economically produced by usingcommercially available plastic tubes, cut to size, having a sufficientmaterial thickness, and custom-lathed plastic lids that are providedwith O-ring seals. The venting valve can be provided in the plastic lid.

1. Method for producing a piston with a cooled ring carrier (1),consisting of a ring carrier part (2) and a sheet-metal part (3) linkedwith it, which forms a cooling channel (4) in connection with the ringcarrier part (2), whereby the cooled ring carrier (1) is Alfin-bonded inan aluminum-base melt before having the piston material cast around it,characterized in that once the ring carrier part (2) and the sheet-metalpart (3) have been linked, the cooled ring carrier (1) is subjected tonegative pressure in a vacuum tank.
 2. Method according to claim 1,characterized in that the cooled ring carrier (1) is vacuum-packed afterremoval from the vacuum tank.
 3. Method according to claim 1,characterized in that the cooled ring carrier (1) is removed from thevacuum-tank only shortly before being dipped into the Alfin bath.